60 MORPHOLOGY AND BVOLDTION
sulcus. Above the insula there lies a short inferior transverse sulcus (I.T.S.)
The calcarine (Ca.S.) and retro-calcarine sulei are continuous, and the collateral sulcus (Co.S.) is simple. The calloso-marginal (C-JI.S.) sulcus is well marked, but the parieto-occipital sulcus is variable.
The olfactory apparatus is small (microsmatism), and the cerebellum appears to be small. The flocculus is smaller than the paraflocculus, which forms the petrosal lobule. The trapezium is not concealed.
The brain is small in some of the Baboons, and its degree of convolution varies in different Cercopithecidae.
The visual area of the neopallium (i.e., all the cerebral cortex apart from the olfactory areas is well developed, and it is more complex than in Tarsius. The eyes have maculae luteae and there is an incomplete optic decussation. So the Cercopithecidse, like the Cebidse, have the complete apparatus for binocular stereoscopic vision. Moreover the tactile sense lodged in the hands is more acute.
PLACENTATION IN THE LOWEE PRIMATES.
Great differences exist in the placentation of the Lower Primates, and it has been shown by Professor J. P. Hill (169), Hubrecht and others that the arrangements in Tarsius resemble those in Man and differ profoundly from those in the Lemurs. The chorion is vascularized through the body stalk in Tarsius and the Anthropoidea, whereas it is vascularized by way of the allantois in the Lemuroidea. The second great difference is seen in the nature of the placenta. In the Lemurs the yolk-sac placenta is a transitory structure, or it is